Signal-control system



Oct. 28, 1930. G. w. CATTELL SIGNAL CONTROL SYSTEM Filed March 27, 1928 2 Sheets-Sheet 1 M m N w Tm e n m Oct. 28, 1930. w, CATTELL I 1,779,585

SIGNAL CONTROL SYSTEM Ffiled March 27, 1928 2 Sheets-Sheet 2 F I I5 E a /4 /2v on non 34 3a 33 f T 4/ 3/ I N V EN TOR Gj/b er 7 I44 Caffel/ A TTORNE YS Patented Oct. 28, 1930 UNITED STATES PATENT OFFICE GILBERT W. CATTELL, OF PALO ALTO, CALIFORNIA, ASSIGNOR T FEDERAL TELE- GRAPH COMPANY, OF SAN FRANCISCO, CALIFORNIA, A CORPORATION OF GALI- FORNIA SIGNAL-CONTROL SYSTEM Application filed March 27, 1928. Serial ll'o. 265,006.

Another object is to smoothly divert the.

energy of a high frequency oscillator from one absorbing circuit to another whereby the load on the oscillator. remains substantially constant. In high frequency signal trans mitting systems, avariety of methods have i been utilized for controlling the supply of high frequency energy to the transmitting circuits. It has previously been proposed to effect direct control of the energy in the transmitting circuit by inserting a key or switch to open or short circuit the same during intervals when no energy is to be transmitted. Such systems are not satisfactory in large installations, because of the inability of switches to carry the relatively high currents involved without sparking of the contacts. A

relatively small amountof sparking interferes with proper transmission of signals, especially where the switch means is employed for coding the energy according to telegraphic signals. Furthermore the controlling of antenna currents in this manner causes a variable load to be placed upon the oscillation generator or other source of high frequency oscillations being utilized.

This invention may be outlined briefly as comprising a pair of oscillatory circuits, one of which is made the transmitting circuit 1n the preferred embodiment of the invention, in combination with a source of oscillatory current coupled to both circuits. In conjunction with the oscillatory circuits, means is provided for distributing the energy supplied from the source to either one of the circuits to the exclusion of the other. scription of this means and of its operation will now be given with the aid of the drawing in which:

Fig. 1 is a circuit diagram illustrating one form of my invention for use with an arc oscillator.

A de- Fig. 2is a circuit diagram illustrating another form of the invention using a vacuum tube oscillation generator.

Figs. 3 and 4: are circuit diagrams illustrating forms of my invention particularly applicable for modulating a carrier wave at an audible rate.

Fig. 5 is a circuit diagram illustrating a modification of'the invention in which the direct current source of 'rid biasing potential have been eliminated.

Referring to Figure 1 for a detailed description of one specific form of my invention, I have shown a pair of oscillatory circuits 11 and 12, the circuit 11 in this instance comprising a radio transmitting circuit, while the circuit 12 is merely an auxiliary ordummy circuit. A. variety of transmitting circuits may be employed, and for simplicity I have shown merely an inductance 13 included in series with the antenna 14 and counterpoise or ground connection 15. The circuit 12 likewise includes inductive and capacitative reactances 16 and 17, c0rresponding to the respective reactances of the trans mitting circuit, and likewise a resistance element 18 corresponding to the resistance of the transmitting circuit.

A suitable source of oscillations 19 is preferably coupled to both circuits, and as an example of a suitable source, I have shown an arc converter 20. Such converters are well known and may comprise a pair of arc electrodes 21 supplied from a suitable source of direct current as indicated by the generator 22. Radio frequency choke 23 is inserted in series with the positive lead from generator 22. For simplicity I have shown the oscillator coupled to circuit 11, as by being connected directly in series with the ground connection. Circuit 12 may be conveniently coupled to the oscillator by having its one terminal, for example the terminal of inductance 16, connected to one side of the oscillator, while the other terminal of circuit 12 is connected to ground 24:.

It is a characteristic of an arc converter or a vacuum tube oscillator that it will generate high frequency oscillations of a frequency corresponding to the oscillatory circuit which it is supplying. Vhcn coupled to two oscillatory circuits, 1 have found that it will oscillate at the frequency of and, supply energy to, that circuit which dissipates the least amount of high frequency energy. hen the dissipating pi'olmrties of two oscillatory circuits are varied oppositely, the irequency of current supplied by the oscillator will change suddenly from the frequency of one circuit to the frequency of the other, and at the same time the energy supplied by the oscillator will likewise be transl'erred rapidly from one circuit to the other.

As I propose to utilize a sudden change in the frequency of converter 19, l pre'icrably tune circuits 11 and 12 to ditlerent but widely divergent frequencies. The impedances of the two circuits are matched as closely as possible. I also propose to vary the energy dissipating properties of the two circuits 11 and 12 by means of a pair of GlQCJlOH relays 31 and 32. These relays may he of the usual three element type, comprising a plate or anode 33, filamentary cathode 34, and grid or control element It is commonly known that with such relays the anode-cathode impedance may be controlled by the potential upon the grid. \Vhen the grid is mace more positive the anode-cathode impedance is decreased. By selecting a proper potential value for grid 35, the anode-cathode impedance may be made practically finite.

Reays 31 and 32 are associated with circuits l1 and 12 in such a manner that the anode-cathode path of each relay is included a controllable impedance element of each circuit. For example as shown the cathodes 34 of both relays are connected to the common conductor 3'? connecting tern'linals of inductances 13 and 16, while the plates 33 are connected to inductances 13 and 16 at points remote from the terminals interconnected by conductor 37.

For controlling the potentials applied to grid 35,1 have shown a C attcry 38, having its positive terminal connected to the cathodes 34, and having its negative terminal connected to both grids thru suitable grid leaks or high resistances 41. Another C battery 43 is provided which has its negative terminal connected to cathodes 34, and its positive terminal connected to the movable contact 44 of a two-way switch 46. The stationary contacts of switch 46 are shown as connected to the grids 35.

Ordinarily C battery is adapted to privide sufiicient negative potential for grids 35, to cause the anodecathodc impedance of the relays to assume an infinite value. However the efiect of connecting C battery 43 to one of these grids, thru the operation of switch 46, causes that grid to assume a positive value, thus causing the anodecathode impedance of that relay to assume a finite value.

l i 'hcn oscillator 19 is in operation, and switch 46 actuated to cause the grid of relay 31 to become positive, then the finite value of the anode-cathode impedance of this relay places a shunt in'ipcdance path across inductance 13, and increases the energy dissipating properties of circuit 11 to the extent that they are greater than the circuit 12, since at that time relay 31 has an infinite impedance due to the fact that grid of this relay has a negative potential. Therefore converter 19 will generate oscillations of the frequency to which circuit 12 is tuned, and substantially all the energy from oscillator 19 will. be diverted to circuit 12 to the exclusion of the transmitting circuit 11. When switch 46 is actuated so as to render the grid 35 of relay 32 positive, and to permit the grid ct relay 31 to become negative, the conditions are re versed and the energy dissipating properties of circuit 12 become greater than those of circuit 11. Therefore the oscillator will immediately change to the frequency to which circuit 11 is tuned, and substantially all energy will be diverted to the transmitting circuit to the exclusion of the auxiliary circuit 12. By operating switch 46 I may therefore control the distribution of energy to the transmitting circuit as desired, either accordin to telegraphic code combinations or at an audible tone frequency, depending upon the manner in which switch 46 is manipulated.

In Fig. 2 I have shown a modification of the invention in which a tube type of oscillator has been substituted for the are converter shown in Fig. 1. In this case the source of oscillations has been shown as being an electron relay 47 having its electrodes associated with suitable reactances for generation of oscillations. For example in the particular type of tube oscillator shown, the grid and plate electroces are shown as connected to terminals of an inductance 43, a mid-point of which is connected to the oathode olt' rel y 47 Inductance 48 is preferably coupled to both the inductanccs i3 and 16 ot the transn'iitting circuit 11, and auxiliary circuit 12. The low potential terminals of inductanccs 13 and 16 are provided with a ground connection 15, and the cathodes of relays 31 and 32 are likewise preferably grounded. Relays 31 and 32 are associated with inductances 13 and 16, in a manner similar to that of Fig. 1. Operation of switch 48 causes the oscillator to change suddenly from one frequency to another, and accordingly causes the energy to either be substantially entirely supplied through the antenna circuit 11, or to the auxiliary circuit 12. It is of course understood that the antenna circuit 11 is tuned to a different frequency from that to which the auxiliary circuit 12 is tuned.

Fig. 3 illustrates a system similar to that of Fig. 1 except in place of switch 46 I have shown a commutating device to distribute the loo Ifll

currents between circuits 11 and 12 at an audible frequency rate, so as to modulate transmitted energy according to a tonefrequency. This commutating device may be conveniently formed by means of a commutating wheel. 51 driven by a motor 52. Engaging segments of this commutator are the brushes 53 and 54 which are connected to the grid 35 of relays 31 and 32 respectively. These brushes are so positioned that when brush 54 is on a conductive segment, brush 53 is on an insulating segment. Therefore when the commutator wheel is rotated, the grids 35 will be caused to alternately assume positive and negative values, so as to distribute the energy between circuits 11 and 12 at an audible frequency rate. For telegraphic purposes the energy supplied by oscillator 19 isthen interrupted according to code combinations as by means of key 55. This key is preferably in the form of a double-pole switch having its arm or blade connected to the positive pole of battery 43, its one contact connected to wheel 51, and its other contact to brush 53.

In Fig. 4 I have shown another system for distributing current between the two oscillatory circuits 11 and 12 at a tone frequency. In this instance the grid of relay 31 is connected to the positive pole of a G battery 56, while the grid of relay 32 is connected to the negative terminal of C battery 57. Included in series with the respective grid circuits of relays 31 and 32, are the inductances 58 and 59, to which is coupled the inductance 61. Oscillator 62 represents a source of audible frequency alternating current which is supplied to inductance 61, and inductances 58 and 59 are so related to inductance 61 that for one half value of the alternating current in inductance 61, the grid of relay 31 is caused to assume a negative value while the grid of relay 32 assumes a positive value, and for the other half cycle the grid of relay 31 is caused to assume a positive value, while the grid of relay 32 assumes a negative value. The alternating current from source 62 may be controlled as by means of a key 63. l Vhcn the key is open, the poling of C batteries 56.

and 57 causes energy to be supplied to the oscillatory circuit 12, rather than to the transmitting circuit 11. To simplify this circuitdiagram, I have diagrammatically indicated an oscillator 64 as a source of high frequency energy.

The system shown in Fig. 5 is similar to that explained with respect to Fig. 1, except that I have shown means for eliminating the C batteries. In this case circuits 11 and 12 have inductances 67 and 68 in common, as the current flow from oscillator 64 is directed thru inductances 67 and 68. These inductances serve as convenient means for securing proper high frequency potentials to impress upon the grids of relays 31 and 32. In

order to opposltely bias these relays, I have shown a double throw double pole switch 66, having its movablecontacts or blades connected to the grids of relays 31 and 32. Conjugate contacts of this switch are'connected to a terminal of inductance 67 while the other two contacts are connected to one terminal of inductance 68. The midpoint between inductances 67 and 68 is preferably connected to the cathodes of relays 31 and 32. Vfith switch 66 in one position, inductance 67 is connected to the grid of relay 31 and inductance 68 to the grid of relay 32, while connections are reversed for the other position of the switch.

The operation of the system shown in Fig. 5 is as follows: Itwill first be assumed that the direction of current flow in this particular instance is thru circuits 11 and 12, thru coil 67, coil 68 to the source 64 and'togroun'd 15.

Under these conditions the plates of relays 31 and 32 will be positive with respect to their cathodes, thereby tending to cause current flow to occur between plates and cathodes of the tubes. At the same instant however the grid 35 of relay 32 is connected to a point on coil 68' which'is more negative than that to which the filaments are connected and therefore at this instance the grid of relay 32 is biased negatively, making the plate filament impedance of tube 32 relatively high. 'The grid of tube 31 at thistime is connected to a point on coil 67 which is positive with respect to the cathode of this relay and therefore at this particular instance the grid of this relay is biased positively with respect to its cathode. Thus the plate cathode impedance of relay 31 at this instance is relatively low or of finite value and being connected across a portion of coil 13 causes the effective A. C.

resistance of circuit 11 to be substantially increased. For this reason at the assumed instant the distribution of current will be into circuit 12. During the next half cycle of the oscillatory current supply from oscillator 64, the plates of both relays 31 and 32 will be negative with respect to their cathodes and therefore there will be no current flow be tween the plates and cathodes due to the rec tifying properties of such tubes. Therefore at this time the respective plate cathode impedances of the tubes are relatively high, and these tubes cause practically no increase in the resistance components of the circuits 11 and 12 with which they are associated. For the complete cycle of the oscillatory currents the average resistance or impedances of the 7 sistance component of circuit 11, so that the flow of energy will be substantially entirely to circuit 11.

The above system of Fig. 5 is desirable in that it permits elimination of C batteries. It is also believed novel in that it utilizes continuously varying potentials for effecting the desired bias.

It will be obvious that the invention de scribed above, presents many advantages over prior systems for controlling distribution of high frequency energ i of signal transmitting circuits. Because of the very small current required for control ing the relays 31 and 32, there can be no sparking of contacts and the signals are rendered distinct and readily readable when received. Furthermore during intervals when no energy is being transmitted to the antenna, the oscillator continues to supply a load and it will therefore remain in more stable operation.

While my system and method operates most effectively with circuits tuned to different frequencies, it is also operative to a practical degree for controlling the distribution of energy to circuits tuned to the same frequency.

I claim 1. In a signaling system, an oscillatory transmitting circuit tuned to one frequency, an auxiliary oscillatory circuit tuned to another frequency, a source of oscillatory energy adapted to supply oscillatory energy at either of said frequencies, and means for varying the energy absorption characteristics of said circuits in an opposite sense whereby energy from said source is either substantially supplied to the signaling circuit at one frequency or is supplied to said auxiliary circuit at a different frequency.

2. In a signaling system, a pair of oscillatory circuits tuned to dilierent frequem-ios, means for supplying energy at either one of said two frequencies to said circui ,s, electron relay means associated with said circuits, and means for controlling said relays oppositely whereby the degree of freedom of said circuits is varied oppositely.

3. In a signaling system, a pair of oscillatory circuits tuned to different frequencies, means for supplying energy at either one of said two frequencies to said circuits, :1. space charge path included in each circuit for varying the degree of freedom of the eel e, and means for controlling said space charge paths in an opposite sense whereby substantially all energy is either supplied at one frequency to one circuit or at the other frerniency to the other circuit.

l. In a signaling system, a relay device comprising an electron emitting cathode, an anode, and a control electrode, a source of alternating current, a radio transmitting circnit aportion of said radio transmitting circuit being included with said source of alternating current in a circuit common to the cathode and anode of said relay device, means in circuit with said source of alternating current for deriving therefrom a potential of like phase to that applied to said anode, other means for deriving a potential of opposite phase to that applied to said anode, and switching means for applying either of said derived potentials to the control electrode.

5. In a signaling system, an electronic relay having a cathode, an anode, and a control electrode, a. source of alternating current, a radio transmitting circuit, a portion of said radio transmitting circuit being included with said source of alternating current in a circuit common to the cathode and anode of said tube, and keying means for applying to said control electrode a potential of the same polarity at any instant as that applied to the anode, or of opposite polarity, whereby said relay is rendered conductive or non-conductive as desired to control the operation of said transmitting circuit.

In testimony whereof I have hereunto set my hand.

GILBERT lV. CATTELL. 

